Lucky for me my interest is mainly limited to trams when it comes to purchasing items, I recently saw an LGB tram minus power bogie on flea bay which sold for about £180. I do know that folk value the LGB tram power truck higher than the Bachmann one but fail to understand how a very basic model can make £180 when it didn't have a power truck, this was definitely a case of it sold for what a buyer would pay.
Live steam I believe has the asking price it does because few people, relatively speaking, build their own live steam models these days. Modelling in any scale from 0 gauge and over has seen a big change in modellers direction of interest, their was a time when most 0 scale modellers were also, to some extent, scratch builders, these days you could have a complete model railway in 0 gauge and not scratch build any track or stock.
What I also think has happened in the last few years, especially with covid lockdown, is more folk have found the hobby and realised there is more to the hobby than just your "Hornby" trainset, this has in turn created a new growing market for people to sell in to and being a new group of followers they are unsuspectingly paying more for items which has pushed the price of second hand items up, I believe the sellers of new models has seen this new source of costumers and this has also pushed up the price of new models.
Suppliers will quote you all sorts of reason for the cost of things going up, material availability because of covid, import duty because of brexit, the willingness of importers and exporters to buy and sell items with britain because of the confusion over the import and export process since 2021, and more. all valid reasons to an extent and something we as modellers just have to live with.
in 2021 I wanted to buy a pair of Bachman trams from a seller in Germany, I didn't purchase the models because of the grief and cost of purchasing the models from Europe, it took a quick look on the www to establish I could have flown to Germany and got a taxi to the sellers house and back home for less than the cost of effectively importing the models.
My own crystal ball, if I had one, would probably suggest that in 4-5 years the market place will settle down, I suspect we will see more suppliers making items available and it wouldn't surprise me if some models which sell for £1,600 second hand today sold for less than this in ten years, just basing this on how things have gone with other scales such as 0 Gauge.
Unfortunately its a sellers market and there isn't a great deal we can do about it. I don't like sounding full of doom and gloom but its the world we live in just now.
David